The present invention relates to a vacuum pump, particularly a vacuum pump of the rotary blower type.
A pump of this type is provided with a connecting line between its suction, or inlet, side and its pressure, or outlet, side as well as with a weighted, or weight biassed, valve which is disposed in this connecting line and opens when a maximum permissible pressure difference is exceeded. With such a valve it is possible to avoid mechanical and thermal overloads on the pump, which occur particularly with rotary blower vacuum pumps if a maximum permissible pressure difference between the suction side and the pressure side is exceeded.
A vacuum pump of this type is described in the catalog of the firm Balzers AG, entitled "Komponenten f/u/ r die Vakuumtechnik" [Components for the Vacuum Art], 1977 edition, at page C8. The rotary blower vacuum pump described therein has an overflow conduit with an overload valve having a vertically oriented sealing element. The drawback of this prior art pump is that it can be operated when oriented to effect pumping in only one conveying direction, namely vertically from top to bottom. The reason for this is the requirements imposed by the weighted overload valve which exhibits the desired characteristics only when oriented in the position shown in the catalogue. In any other installation position, it cannot operate properly.
German Offenlengungsschrift [Laid-open Application] No. 1,939,717 discloses a rotary blower pump of such a design that it can be operated while oriented to have either a vertical or a horizontal conveying direction. For the reasons described above, a weighted valve of the type described earlier herein cannot be used in this rotary blower pump. It would be conceivable to use a valve whose operation is independent of pump orientation, for example a spring biassed valve, instead of the weighted valve. However, such valves have considerable drawbacks when used as overload valves.
In rotary blower pumps with bypass lines provided with spring biassed overload valves, there frequently occur strong self-induced flow pulsations in the system constituted by the rotary blower pump and the overflow line, and with a spring biassed valve such flow pulsations may result not only in loud noise but also in considerable vibration and hammering of the valve, leading to destruction of the pump and of the valve. The reason for this, obviously, is that a rotary blower pump having an overload line can act like an amplifier with feedback, the rotary blower pump acting as the amplifier and the overload line with the spring biassed overload valve acting as the feedback.
Drawbacks of this type are rarely exhibited by weighted overflow valves. Their drawback, however, is their position dependence so that a prior art vacuum pump equipped with such a valve can be operated only when oriented to effect pumping in one conveying direction.